<html>

<head>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/css/bootstrap.min.css" integrity="sha384-Zug+QiDoJOrZ5t4lssLdxGhVrurbmBWopoEl+M6BdEfwnCJZtKxi1KgxUyJq13dy" crossorigin="anonymous">
    <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/js/bootstrap.min.js" integrity="sha384-a5N7Y/aK3qNeh15eJKGWxsqtnX/wWdSZSKp+81YjTmS15nvnvxKHuzaWwXHDli+4" crossorigin="anonymous"></script>

    <style>
        .doc {
            width: 170px;
            height: 220px;
            background-color: lightgrey;
            margin: 10px;
        }
    </style>

</head>

<body>
<h1>Hello, world!</h1>

<div class="">

    <div class="d-flex align-content-between flex-wrap">
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>
        <div class="doc"></div>


    </div>

</div>
</body>
</html>
